Terry J. Peek wrote:
> I am trying to differentiate between Serratia marcescens and a gram pos. cocci
> that I suspect is Staph epidermidis or S. aureus. I've placed the culture on
> 10% NaCl agar. I'll check the results later this morning. What is the best way
> to seperate these organisms using the resources of a small college lab? Is my
> first step in the right direction? Any suggestions would be appreciated.
> Thanks. Terry
Terry,
There are lots of differences between Serratia marcescens and the two cocci you
mentioned. If you know an organism is one of these three species, it is
relatively easy to distinguish Serratia marcescens. Many strains of Serratia
marcescens when grown as surface colonies produce a red pigment (in contrast,
Staphylococcus epidermidis is usually light colored and Staphylococcus aureus is
usually dark yellow or golden (the species epithet refers to gold). The color of
colonies is really not very taxonomically significant (in fact, <90% of Serratia
marcescens strains produce the red pigment), but if you want a quick and dirty
discriminator, this may be it. From a taxonomic standpoint, probably the most
reliable differentiating characteristics are morphological: Serratia are
gram-negative rods, whereas staphylococci are gram-positive cocci, often arranged
in grape-like clusters.
--
David R. Boone
Professor of Environmental Microbiology
Oregon Graduate Institute, Portland
503-690-1146
boone at ese.ogi.eduhttp://www.ese.ogi.edu/ese_docs/boone.html
